During three cruises in the Mid Atlantic Ridge area in 2016 and 2017, we studied the biomass of mesopelagic fish down to a depth of 600 m and identified and quantified the species composition of the catches. The biomass density was estimated considering the volume of water filtered by the cross-sectional area of the trawl blinded with 16 mm meshes (130 m–2), the distanced covered by the trawl (m) at a towing speed (transformed to m s–1) the effective tow time (min) and the catch (kg).